The proposed research will use the case of the Irish at the beginning of the twentieth century to investigate several explanations offered for the timing and pace of the European fertility transition. We will construct a sample from the manuscript schedules of the Irish census of 1911 and use already-extant samples from the U.S. census of 1910 to examine the roles of religion, class, migration, and neighbors in the Irish fertility transition. All of these factors have been advanced in varying ways as explanations for aspects of the fertility transition historically and in developing countries today. The Irish at the turn of the twentieth century offer an excellent opportunity to test these explanations because of the special features of the Irish population at the time. The Irish sample will be drawn from the cities of Dublin and Belfast. Rural Ireland has been studied much more extensively, and the urban Irish exhibit more religious and class heterogeneity. Most Irish-Americans also became urban dwellers, focusing our comparison of the emigrant population. All original datasets generated in the course of this research will be made available on websites. The Irish census and its U.S. counterpart asked married women how long they had been married, how many children they had, and how many survived. Using this intriguing source will require an extension of econometric models intended for use with "count" data. These models are applicable in a number of demographic studies, so the methodological aspect of this research will be of wider use. We will develop specialized software for our own research and make that software available to other researchers.